What would be the equivalent P.S.I. reading of a 400EX with a standard bore Wiseco 10:1 piston?

 

In a perfect world, it would be 147 psi at sea level with 0 percent humidity and 59 degrees F, or if you prefer 15 C. But it's not a perfect world, so my guess would be around 130-140 at Sea level. As altitude increases the pressure will be lower.

 

Is that psig, or psia, minehunter? ("g" for gauge, "a" for absolute.) I don't know; at bdc, psig is zero; psia (sea level, standard temperature and barometric pressure) is 14.7. At tdc on the compression stroke? Lemme think!

You're quite correct about the imperfect world, containing ring blow-by, valve leakage; even intake valve duration sometimes affecting pressure readings.

I think your numbers, both the theoretical and the practical, are pretty close to valid.

Tree Farmer

 

Thanks a lot guy's you helped me decide what piston to buy cause race gas is hard to buy in the Philippines.